In one form of a process for the production of corrugated plastic tubes, a plastic material is passed by means of an extrusion device through an injection head into a mold section which is formed by movable mold jaws and in which the plastic material is caused to bear in molding contact thereagainst by virtue of a reduced external pressure and/or an increased internal pressure. A suitable apparatus for carrying that process into effect comprises the extrusion device connected to at least one injection head with which there is operatively associated a mold section having the movable mold jaws.
Hitherto in such apparatuses the injection head and the mold section operatively associated therewith, having the movable mold jaws, are always arranged horizontally. Such a design configuration can only be used for corrugated plastic tubes of a given maximum outside diameter because, in the molding procedure, progressively more plastic material has to be blown or sucked into the mold jaws by the reduced external pressure or by the increased internal pressure, in the region of the mold section, in particular in the upper part or in the upper third of the fresh corrugated plastic tube, as a result of the increasing wall thickness thereof. In that situation problems arise not only due to the fact that ever increasing pressure or suction forces are required for correspondingly larger amounts of plastic material for corrugated tubes of correspondingly large diameter, but also by virtue of the fact that corrugated tubes of correspondingly large diameter can also be produced only at a suitably reduced extrusion rate. Furthermore, in the case of the previous procedures as outlined above which are implemented in a horizontally oriented mold section when producing corrugated plastic tubes of relatively large outside diameter, the corrugation spacings of adjacent corrugations of the corrugated tube are limited in the decreasing direction, that is to say they are required to be correspondingly large, and that is often something that is not wanted. A further deficiency of the above-outlined previous processes and apparatuses is that leakage effects between the mold jaws and the plastic material when using vacuum or leakage effects between a central calibration or sealing bar or mandrel and the plastic material when using an increased internal pressure, that is to say when effecting a pressure calibration operation, progressively increase, by virtue of the relatively large dimensions of the corrugated plastic tubes. Due to the extrusion rate being relatively low, as already referred to above, the leakage condition also referred to above persists for a correspondingly prolonged period of time, and that is a further deficiency which cannot be disregarded.
DE 36 22 775 C2 discloses an apparatus for the production of ribbed tubes from a moldable material, the tubes having a smooth inside surface. That arrangement has a core region comprising a spindle, a conically enlarging bar or mandrel which is disposed downstream of the spindle in the production direction of the arrangement and a core disposed downstream of the bar or mandrel and being of a substantially constant diameter. The spindle is surrounded by a mouthpiece sleeve which together with the core region forms a mouth for the plastic material. The mouthpiece sleeve and the core region form chill molds which can be conveyed along an endless path and which at their inside surface have grooves, more specifically for shaping ribs on a tube, while an end zone of the core which is at a spacing from the above-mentioned mouth has means for cooling that zone. In that arrangement the core can be cooled by means of a liquid coolant.
DE 31 20 480 A1 discloses an apparatus for the production of plastic tubes having transverse grooves or channels. In that apparatus half-molds which are provided with a molding cavity and which supplement each other in pairs at a mold section to constitute a respective mold are arranged to be circulated on a machine table, wherein arranged upstream of the mold section is an injection head of an extruder and wherein the half-molds are provided with vacuum ducts communicating with the respective mold cavities. The vacuum ducts open in the mold section at vacuum connections provided in the machine table. The half-molds are provided with cooling ducts which communicate in the mold section with cooling water feed means and discharge means which are also provided in the machine table. In order to ensure precise temperature setting for the half-molds during operation of the apparatus the cooling ducts and the vacuum ducts in the respective half-molds are completely separated from each other.
JP Abstract No 59-131433 discloses a process and an apparatus for the production of perforated tubes or perforated ribbed tubes, wherein a punch member which is disposed in a downwardly hanging position can be moved up and down in relation to a bottom tool portion in order thereby to define a correspondingly variable annular gap through which a plastic material is extruded. In that arrangement the respective tube being produced is extruded perpendicularly downwardly.
German published specification (DE-AS) No 1 039 741 describes an apparatus for the fine processing of elongate plastic components such as for example a tube, a hose, a strip or the like, in which the component is passed while still in a plastic condition from an extrusion press through a pressing mouthpiece member of a configuration corresponding to the required definitive shape, into a cooling and hardening bath. There, a stationary or rotating bar or mandrel which is mounted within the mouthpiece member projects through the shaping tool into the interior of the container in which the cooling and hardening bath is disposed. In that arrangement the mouthpiece member is oriented horizontally, in other words the respective component is passed into the cooling and hardening bath horizontally, which signifies that the force of gravity can have a corresponding effect thereon.
German published specification (DE-AS) No 1 280 552 discloses an apparatus for the continuous production of transverse grooves or channels, bulge portions or the like on a tube of thermoplastic material issuing from an extrusion press. The apparatus has a longitudinally divided hollow mold which affords the required profile and which can also be moved with the tube. That mold comprises a plurality of mold portions which are joined together to form two rows and which are provided with guide members such as rollers or the like. The guide members engage into suitable guide tracks by which the mold portions are brought together along the molding region of the apparatus to constitute a closed mold. For the purposes of pressing the tube to be shaped against the interior of the mold the apparatus has a nozzle for the introduction of a pressure medium into that part of the tube. The mutually facing end faces of the individual mold portions bear against each other when the mold portions are being guided in a straight line, wherein the geometrical pivot axes of the mold portions which at the same time form the geometrical axes of the guide members are arranged in the central plane of the end faces of the mold portions of a row, said end faces being in mutually adjacent relationship in the closed condition of the mold.
German published specification (DE-AS) No 1 248 913 discloses an apparatus for the production of corrugated plastic tubes, wherein a device for producing the corrugations is disposed adjoining an annular nozzle of an extrusion press for extruding the tubes. The corrugating device comprises individual dies which supplement each other to afford the desired tube shape and which are brought together in front of the annular nozzle to form a closed tubular mold passage which is provided with corrugation configurations. A device which is held by the mouthpiece member of the extrusion press projects into the mold passage, to expand the tube which is extruded from the press. The dies comprise rotatably mounted, synchronously drivable mold disks whose axes of rotation are arranged on a circle around the mold passage to be formed and whose peripheral surfaces are profiled to correspond to the desired corrugation configuration.
The use of a transverse cutter which is moved simultaneously with an elongate plastic component, for severing that components to be found for example in the German journal: GAK 4/1977 pages 200 through 204.